1. Field of the Invention
This invention relates generally to a system and method for warning the driver of a vehicle that an active control system on the vehicle is taking action and, more particularly, to a system and method for warning a driver of a vehicle that an active control system on the vehicle is taking action, or other driver alertness condition needs to be brought to the drivers attention, that includes dithering the steering wheel of the vehicle.
2. Discussion of the Related Art
Modern vehicles sometimes incorporate active vehicle control systems. One such system is known as a vehicle stability enhancement (VSE) system that assists the vehicle operator in providing vehicle handling on surfaces such as wet or uneven pavement, ice, snow or gravel. The VSE system typically senses wheel skid based on inputs from a wheel speed sensor, a steering angle sensor, a vehicle speed sensor and a vehicle yaw rate sensor. The VSE system uses these inputs to reduce engine torque and apply differential braking to help maintain the vehicle travel along the intended path.
Additionally, active chassis control systems have been emerging in the art that are used in combination with VSE systems. The chassis control systems typically include differential braking control, real-time suspension damping, automatic rear-wheel steering and active front steering control. With the capability of controlling chassis dynamics in real time, the active chassis control systems can be used to enhance the vehicle handling performance.
Another active vehicle control system is known as an active front steering (AFS) system that provides automatic front-wheel steering. AFS systems typically employ a steering actuator system that receives a steering signal from a hand-wheel angle sensor, a vehicle speed signal and a vehicle yaw rate signal, and provides a correction to the operator steering signal to cause the vehicle to more closely follow the vehicle operator's intended steering path to increase vehicle stability and handling. The AFS system is able to provide steering corrections much quicker than the vehicle operator's reaction time, so that the amount of operator steering is reduced. The AFS system provides a more direct vehicle steering under normal road conditions at low and medium speeds, reducing operator steering effort. The AFS system also may help to increase vehicle agility in city traffic or during parking maneuvers. The AFS system also provides less direct vehicle steering at higher vehicle speeds.
The stability control systems discussed above may provide vehicle stability control in response to driver aggressiveness and/or road conditions when needed. Because the stability control system typically controls the vehicle in the way the driver intends, the driver may not be aware that the control system is actively providing stability control. Therefore, the driver may not take appropriate action or care, such as reducing driving aggressiveness, in response to the stability control action. Thus, it would be desirable to provide some type of indication or warning to the driver that the stability control system was active.